Small two-stroke engines enjoy widespread acceptance in the field of hand-held outdoor equipment due to performance advantages over competing technologies. The main issue with these engines is a potential for high hydrocarbon emissions. In traditional two-stroke engines, incoming fuel mixture (fuel and air) is used to help expel exhaust gases. With stratified scavenging, a fresh air charge is used to expel the exhaust gases. The result is lower emissions and lower fuel consumption.
In a stratified scavenging two-stroke internal combustion engine, an air supply is introduced into a combustion chamber of the engine after a combustion event has occurred and before a fuel mixture is delivered from a crankcase chamber of the engine. The air supply facilitates exhausting the combusted gas from the combustion chamber and provides some air to facilitate combustion of the subsequently delivered fuel mixture.